An experiment is described which seems to indicate that line spectra of analysis elements and the associated background are excited concurrently in an ac arc. If, for the analysis of plant and biological materials, an ac arc is used as light source, the intense OH band spectrum covering the wavelength region 3063-3300 Å is best resolved by arcing the sample in an atmosphere of oxygen Carbon dioxide is unsatisfactory. The gas environment of an ac arc influences its spectral characteristics and spectra excited in oxygen and carbon dioxide atmospheres are much more spark-like than spectra excited in air Of the arc parameters, viz electrode separation and arc current, the latter is the more critical and arc currents must be regulated to .1 ampere.
A. Strasheim, "The Dependence of Background Associated With High Voltage AC Arc Spectra on Certain Parameters," Appl. Spectrosc. 11, 76-83 (1957)